1. Field of the Invention
This invention relates to a rotation sensor for generating electric signals corresponding to rotation angle and rotation direction of a steering wheel which is connected to, for example, a steering shaft of an automobile.
2. Description of Related Art
FIG. 42 to FIG. 46 describe a prior art rotation sensor. The rotation sensor 61 comprises a base 62 fixed at the suitable static position, a rotor 69 which rotates together with a connector 63 with respect to the base 62, a speed reduction rotor 71 which is engaged rotatably with the rotor 69, a gear mechanism 73 provided between the rotor 69 and speed reduction rotor 71, and a composite board 64 supported by the base 62.
The base 62 is formed of plastic material having a circular shape in the plan view and is provided with a hole 62a at the center. The base 62 has a ring-shaped outside peripheral wall 62b on the peripheral edge on the under side and a ring-shaped inside peripheral wall 62d along the periphery of the hole 62a.
The connector 63 is formed of plastic material having a cylindrical shape. The connector 63 with a pair of projections 63a on the top end and an engagement projection 63b on the bottom side of the outside peripheral wall. The connector 63 is inserted into the hole 62a of the base 62 and the pair of projections 63a are extended beyond the top surface of the base 62 upward. The engaging projection 63b is extended beyond the inside peripheral wall 62d of the base 62 downward.
The composite board 64 is a circular disc formed of insulating material and has a hole 64a at the center, and on the bottom surface is provided with endless ring electrode patterns 65 and 66, a first resistor pattern 67 positioned inside the electrode pattern 65, and a second resistor pattern 68 positioned outside the electrode pattern 66, which are all formed by printing (in FIG. 43, slant line bands are drawn on patterns 65-68). The composite board 64 is provided with terminals 65a and 66a connected to the respective electrode patterns 65 and 66, with terminals 67a and 67b connected to both ends of the first resistor pattern 67, and with terminals 68a and 68b connected to both ends of the second resistor pattern 68. The composite board 64 is supported in a recess 62c of the base 62 with its bottom surface exposed, wherein the connector 63 and the inside peripheral wall 62d are inserted into the hole 64a.
The rotor 69, which is provided on the under side of the base, is a ring formed of plastic material having an engagement groove 69a on the inside peripheral surface and having an arm 69b which supports a first brush 70 on the outside peripheral surface. The connector 63 is inserted into the rotor 69 to engage the engagement projection 63b of the connector 63 with the engagement groove 69a of the rotor 69, and the rotor 69 is thereby supported on the base 62, and thus the rotor 69 is rotatable together with the connector 63 with respect to the base 62 wherein the first brush 70 bridges between the conductive pattern 65 and the first resistor pattern 67.
The speed reduction rotor 71 is a disk formed of insulating material having a hole 71a at the center and having a supporting shaft 71b on the top surface. The supporting shaft 71b of the speed reduction rotor 71 is positioned in the recess 62c of the base 62 so that the bottom end of the rotor 69 is engaged rotatably with the hole 71a, and the speed reduction rotor 71 is supported by the base 62 rotatably around the rotor 69 wherein the second brush 72 bridges between the conductive pattern 66 and the second resistor pattern 68.
The gear mechanism 73 comprises a planetary gear mechanism comprising a sun gear 74 formed on the outside peripheral surface of the rotor 69, an inside gear 75 formed on the inside peripheral surface of the outside peripheral wall 62b of the base 62, and a planetary gear 76 comprising a double gear supported rotatably by the supporting shaft 71b of the speed reduction rotor 71. A small diameter pinion 76a positioned on the upper stage of the planetary gear 76 is engaged with the inside gear and the large diameter pinion 76b positioned on the lower stage is engaged with the sun gear 74 so that the rotation of the connector 63 is converted to the revolution of the planetary gear 76 and the revolution is transmitted to the speed reduction rotor 71. In this system, the speed reduction ratio is set at approximately 1/4, therefore, the speed reduction rotor 71 makes a turn together with the second brush 72 at every four turns of the connector 63 together with the rotor 69 and the first brush 70.
The rotation sensor 61 structured as described herein above has the first absolute type encoder 77 comprising the first brush 70, the electrode pattern 65 and the first resistance pattern 67, and the rotor 69, and has the second absolute type encoder 78 comprising the second brush 72, the electrode pattern 66 and the second resistance pattern 68, and the rotor 69.
The rotation sensor 61 is used, for example, in an automobile. The base 62 is fixed to a suitable stationary portion such as a steering column, and a steering shaft is inserted into the connector 63, the pair of projections 63a of the connector 63 are engaged with the recess on the steering wheel 79 side as shown in FIG. 42 so that the connector 63 is rotated together with the steering wheel 79.
At that time, the first brush 70 bridges between the middle point (C1 point in FIG. 43) of the first resistance pattern 67 and the electrode pattern 65 when the steering wheel 79 is positioned at the neutral position. Therefore, when the steering wheel 79 is positioned at the neutral point, the resistance value between the terminals 65a and 67a is equal to the resistance value between the terminals 65a and 67b, however when the steering wheel 79 is turned right or left the above-mentioned resistance values change.
The resistance value increases linearly with a right turn of the steering wheel 79 (a turn in the direction of the arrow D in FIG. 43) and decreases linearly with a left turn of the steering wheel. In this case, a constant voltage Vc (the terminal 67b is the ground potential) is applied between the terminals 65a and 67b, and the first voltage signal 80 which varies as shown with a solid line in FIG. 44 correspondingly to the turn of the steering wheel 79 is generated between the terminals 65a and 67b.
In detail, the first voltage signal 80 varies from 0 to Vc at every turn of the steering wheel 79, and the turning angle and turning direction of the steering wheel 79 are detected thereby. The no signal area X between adjacent first voltage signals 80 is due to the disconnection between the first resistance pattern 67 and the electrode pattern 65 generated when the first brush 70 is positioned between the terminals 67a and 67b.
On the other hand, when the steering wheel 79 is position at the neutral position, the second brush 72 bridges between the middle point (C2 point in FIG. 43) of the second resistance pattern 68 and the electrode pattern 66. Therefore, when the steering wheel 79 is positioned at the neutral position, the resistance value between the terminals 66a and 68a is equal to the resistance value between the terminals 66a and 68b. The above-mentioned resistance values change correspondingly to a right turn or a left turn of the steering wheel 79.
As set forth above the resistance value increases linearly with a right turn (turn in the direction of the arrow D in FIG. 43) of the steering wheel 79 or decreases linearly with a left turn of the steering wheel 79. Also in this case, a constant voltage Vc (the terminal 68b is the ground potential) is applied between the terminals 68a and 68b, and the second voltage signal 81 which varies as shown with a chain double-dashed line in FIG. 44 is generated between the terminals 66a and 68b corresponding to the turn of the steering wheel 79.
The second voltage signal 81 varies from 0 to Vc at every four turns of the steering wheel 79, and the turning angle and turning direction from the neutral position of the steering wheel 79 are detected based on the variation of the second voltage signal 81.
FIG. 45 shows a schematic circuit structure for processing the above-mentioned first and second voltage signals 80 and 81. Switches 82 and 83 are analogue switches which become conductive only when the gate terminal receives a high level signal, the one switch 82 is positioned between the first absolute type encoder 77 and an output terminal 84, and the other switch 83 is positioned between the second absolute type encoder 78 and the above-mentioned output terminal 84.
A discrimination circuit 85 is structured so that the discrimination circuit 85 receives a second voltage signal 81 from the second absolute type encoder 78 and generates a discrimination signal Sd (high level signal) only when the turning angle of the steering wheel 79 indicated by means of the second voltage signal 81 is within .+-.45 degrees. The above-mentioned discrimination signal Sd is supplied directly to the gate terminal of the switch 82 and also supplied to the gate terminal of the switch 83 by way of an inverter 86.
Because the discrimination circuit 85 is structured as described herein above, if the turning angle of the steering wheel 79 from the neutral position is within 45 degrees, the switch 82 becomes conductive and a first voltage signal 80 from the first absolute type encoder 77 is sent out through the output terminal 84. On the other hand, if the turning angle of the steering wheel 79 from the neutral position is in the range outside .+-.45 degrees, the switch 83 becomes conductive and a second voltage signal 81 from the second absolute type encoder 78 is sent out through the output terminal 84.
In other words, a signal which has been formed by synthesizing a first and second voltage signals 80 and 81 as shown in FIG. 46 is generated as the steering wheel 79 is turned. The signal from the output terminal 84 (the signal which indicates the turning angle and the turning direction from the neutral position of the steering wheel 79) is used for suspension control and automatic transmission control of an automobile.
The second voltage signal 81 from the second absolute type encoder 78 varies linearly even when the steering wheel 79 is made a plurality of turns, as the result the turning angle and the turning direction from the neutral position of the steering wheel 79 are detected in real time based on the above-mentioned second voltage signal 81. However, the above-mentioned second voltage signal 81 is disadvantageous in that the variation magnitude per turning angle of the steering wheel 79 is small and the resolution, namely accuracy, is low because the second voltage signal 81 is obtained by reducing the turning of the steering wheel 79.
On the other hand, because the first voltage signal 80 generated from the first absolute type encoder 77 is obtained from the rotor 69 which is rotated together with the steering wheel 79, the accuracy of the turning angle information and the turning direction information of the steering wheel 79 obtained based on the first voltage signal 80 is high though it is disadvantageous in that the neutral position of the steering wheel 79 can not be specified.
Accordingly, the mutually complemental use of the first and second voltage signals 80 and 81 as shown in FIG. 45 allows us to detect the turning angle from the neutral position of the steering wheel 79 over the wide range at high accuracy in real time. In the range of turning angle of the steering wheel 79 (in the range within .+-.45 degrees) where high accuracy is particularly required, the use of the first voltage signal 80 as described herein above allows us to control the suspension and automatic transmission of an automobile accurately.
However, the above-mentioned prior art rotation sensor is disadvantageous in that there is some range where the second voltage signal 81 can not be complemented by the first voltage signal 80 and all the ranges can not be complemented by the first voltage signal 80, and as the result the turning angle of the detection target such as the steering wheel 79 can not be detected accurately and in real time over the wide range because there is a no signal area X between adjacent first voltage signals 80.